Invalid Key Exception - encryption

Question

I am retrieving a text password as input from a file and applying AES encryption over that and later on, decrypting that.
When I did it for the first time, every 4 out of 5 times it was running correctly (encryption decryption successful) but 1 time, it was throwing BadPaddingException. Following is what I wrote :
//ABCD is class name
public static void enc(String fileName, String pwd) {
try {
Properties prop = new Properties();
InputStream input = ABCD.class.getClassLoader().getResourceAsStream(fileName);
prop.load(input);
input.close();
URL url = ABCD.class.getClassLoader().getResource(fileName);
FileOutputStream outputStream = new FileOutputStream(url.getPath());
KeyGenerator key = KeyGenerator.getInstance("AES");
key.init(128);
SecretKey aesKey = key.generateKey();
String newkey = new String(Base64.encode(aesKey.getEncoded()).getBytes("UTF-8"));
Cipher aesCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
aesCipher.init(Cipher.ENCRYPT_MODE, aesKey);
byte[] clear = pwd.getBytes("UTF-8");
byte[] cipher = aesCipher.doFinal(clear);
String encPwd = new String(cipher);
prop.setProperty("password", encPwd);
prop.setProperty("secKey", newkey);
prop.store(outputStream, null);
outputStream.close();
} catch (Exception e) {
System.out.println(e);
}
}
public static String dec(Properties prop, String fileName) {
String decPwd = ABCD.map.get(fileName);
try {
String newkey = prop.getProperty("secKey");
StringBuilder pwd;
byte[] newkeybuff = Base64.decode(newkey.getBytes("UTF-8"));
SecretKey key = new SecretKeySpec(newkeyuff, "AES");
Cipher aesCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
aesCipher.init(Cipher.DECRYPT_MODE, key);
pwd = new StringBuilder(prop.getProperty("password"));
byte[] cipher = aesCipher.doFinal(pwd.toString().getBytes());
decPwd = new String(cipher);
} catch (Exception e) {
System.out.println(e);
}
ABCD.map.put(fileName, decPwd);
return decPwd;
}
I needed to fix this. Somewhere, I read that BadPaddingExcpetion occurs since of the operations done with String, in place of where actually byte should be used. Hence, I changed my code to the following :
public static void enc(String fileName, String pwd) {
try {
Properties prop = new Properties();
InputStream input = ABCD.class.getClassLoader().getResourceAsStream(fileName);
prop.load(input);
input.close();
URL url = ABCD.class.getClassLoader().getResource(fileName);
FileOutputStream outputStream = new FileOutputStream(url.getPath());
KeyGenerator key = KeyGenerator.getInstance("AES");
key.init(128);
SecretKey aesKey = key.generateKey();
byte[] newkey=(Base64.encode(aesKey.getEncoded())).getBytes("UTF-8");
Cipher aesCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
aesCipher.init(Cipher.ENCRYPT_MODE, aesKey,new IvParameterSpec(new byte[16]));
byte[] clear = pwd.getBytes("UTF-8");
byte[] cipher = aesCipher.doFinal(clear);
prop.setProperty("password", Arrays.toString(cipher));
prop.setProperty("secKey", Arrays.toString(newkey));
prop.store(outputStream, null);
outputStream.flush();
outputStream.close();
} catch (Exception e) {
System.out.println(e);
}
}
public static String dec(Properties prop, String fileName) {
String decPwd = ABCD.map.get(fileName);
try {
byte[] newkey=prop.getProperty("secKey").getBytes("UTF-8");
byte[] pwd;
byte[] newkeybuff = Base64.decode(newkey);
SecretKeySpec key = new SecretKeySpec(newkeybuff, "AES");
Cipher aesCipher=Cipher.getInstance("AES/CBC/PKCS5Padding");
aesCipher.init(Cipher.DECRYPT_MODE, key,new IvParameterSpec(new byte[16]));
pwd = prop.getProperty("password").getBytes();
byte[] cipher = aesCipher.doFinal(pwd);
decPwd=new String(cipher);
System.out.println("Decrypted pwd " + decPwd);
}
catch (Exception e) {
System.out.println(e);
}
ABCD.map.put(fileName, decPwd);
return decPwd;
}
Now, I am getting InvalidKeyException. This time, I read that the size of the key should be 16 bytes. But I don't know how to apply this. Need a fix for this!

Answer 1

You should check your IV (Initialization Vector) which must be the same for encryption and decryption.

Answer 2

A padding error usually means the decryption failed.
Check that the key is a full length (16, 24 or 32 bytes), the IV is full length (16-bytes). If the key or IV is to short it will be padded with "something"and that man not be consistent, there is no standard for such padding.
getBytes("UTF-8") may return different length of bytes depending on the characters used.
Using new IvParameterSpec(new byte[16]) for the IV is incorrect, the IV should be a random bytes. A usual method of handling the IV is to create a random IV on encryption and prepend it to the encrypted data, it does not need to be secret and by prepending it will be available for decryption.